OTP means One-time password, also called dynamic password, it is a time-dependent and unpredictable random digital combination generated according to special algorithm in every 60 seconds. Each password can only be used once. OTP can be technically divided into three types, that is, time synchronization, event synchronization, and challenge/response, of which, the challenge/response OTP is typically used in online business, a challenge code is output from a server terminal to a website/response, and the challenge code is input into a dynamic token, and a 6/8-bit random digits is generated by an internal algorithm, the password is available for once, and because it is required to input the challenge code, a digital keyboard is required.
For a composite device possessing both the OTP function and the USBKEY function in the prior art, an OTP control chip is used to control a display and keys. When using a USB interface, an USB control chip communicates with the OTP control chip via an additional communication port and transmits contents to be displayed to the OTP control chip for displaying by the displayer, and key press information is transmitted to the USB control chip via the OTP control chip. When using the USB mode, the OTP control chip communicates with the USB control chip, the OTP control chip needs to operate at relatively high speed, and there are two power supply methods in the prior art, one method is to use a battery of the OTP control chip to supply power, in this way, the power of the battery of the OTP control chip will be consumed in the USB mode, in order to ensure enough service time in the OTP mode, the capacity of the battery is required to be increased, thereby increasing the cost of the battery, moreover, once a device is connected with the USB interface for a long period, the battery may be depleted; the other method is to automatically switch to an USB interface for power supply in the USB mode, the method requires complicate switching circuit, moreover, voltage instability of the USB interface may induce reset of the OTP control chip, thereby making the OTP function ineffective. Both the two methods frequently start the OTP control chip when using the USB interface function, and when communication error occurs, the abnormal operation of the OTP control chip may be caused, which makes the OTP mode unavailable, and if the OTP control chip operates abnormally, the USB mode may also be unable to operate. In summary, there are problems in the prior art that when using the USB mode and switching to the USB interface for power supply, the instability of the power supply by the USB interface may make the OTP control chip lose the preset contents and require increase of the capacity of the battery.